This invention relates to a structure of a cap seal in a reservoir tank for storing hydraulic fluid to be used in a master cylinder.
A known type of reservoir tank 1 is illustrated in FIG. 1, which is adapted to be mounted on an upper surface of a master cylinder (not shown) for storing hydraulic fluid. Formed at the lower part of the inside of the reservoir tank 1 is a rib 3, on the upper end surface of which a hat-shaped strainer 5 having a rib 4 formed therein is disposed. A cap 8 is threaded onto the upper portion of the outer periphery of the reservoir tank 1 in such a manner to cover the upper opening of the reservoir tank 1. A seal case 9 fitted to the interior side of the cap 8 comprises a disk-shaped base 10, a cylindrical cap seal container 11 formed on the outer end of the base 10, and a disk-shaped baffle 12 formed on the lower surface of the base 10. Formed on the outer periphery of the cap seal container 11 is an annular channel 13 in which a cap seal 14 is received so as to resiliently contact with the inner periphery of the reservoir tank 1 when the cap 8 is engaged with the reservoir tank 1.
However, there are drawbacks in a structure of the conventional reservoir tank 1 for the master cylinder of this type. Due to jerking or jolting of a vehicle body, hydraulic fluid 2 may splash against and may adhere to the base 10 and the baffle 12. As a result, when an inspector removes and tilts the cap 8 for the purpose of inspecting the inside of the reservoir tank 1, the hydraulic fluid 2 adhering to the base 10 and baffle 12 may drip on a female thread section of the cap 8 as shown in FIG. 2. Therefore, when the cap 8 is again threaded onto the reservoir tank 1, the hydraulic fluid 2 which adheres to the female thread section may drip on and run down along the outer periphery of the reservoir tank 1. This may lead to a misunderstanding that the hydraulic fluid 2 might have leaked out from the reservoir tank 1.
To overcome this problem, there has been proposed a cap seal which has an annular or cylindrical projection a tip of which projects closer to the hydraulic fluid side than the lower end surface of the cap 8, thereby preventing hydraulic fluid 2 adhering to the base 10 and the baffle 12 from dripping on and adhering to the internal thread section of the cap 8 even when the cap 8 is removed and tilted as shown in FIG. 2. Such cap seal having the annular or cylindrical projection is detailed in copending U.S. Pat. No. 4,514,984, filed on June 13, 1983 which is assigned to the assignee of this application and incorporated herein by reference.
Although successful in eliminating the misunderstanding, since the tip of the projection comes in contact with the strainer 5, a space defined by the reservoir tank 1, the strainer 5 and a surface of the hydraulic fluid 2, which may be viewed from the outside of the reservoir tank 1, is completely sealed by the cap seal. This causes the level of the hydraulic fluid 2 in the reservoir tank 1 to be lowered by means of the air sealed therein or raised due to negative pressure of the sealed air and therefore the level is viewed as being lower or higher than the actual or true level of the hydraulic fluid 2 in the reservoir tank 1, respectively, which might lead the inspector to misunderstand the amount of the hydraulic fluid 2 in the reservoir tank 1. In order to solve this problem, a gap may be provided between the tip of the projection and the upper surface of the strainer 5 thereby permitting an escape of the air in the space. In this case, however, since the strainer 5 must be lowered to provide the gap, the capacity of the reservoir tank 1 may be reduced.